
function httpGetAsync(theUrl, callback){     
    var xmlHttp = new XMLHttpRequest();
     xmlHttp.onreadystatechange = function() {
               if (xmlHttp.readyState == 4 && xmlHttp.status == 200)             callback(xmlHttp.responseText);    
                }    
                xmlHttp.open("GET", theUrl, true); // true for asynchronous      
                xmlHttp.send(null);}


function httpGet(theUrl){
var httpRequest = new XMLHttpRequest();//第一步：建立所需的对象
        httpRequest.open('GET', 'url', true);//第二步：打开连接  将请求参数写在url中  ps:"./Ptest.php?name=test&nameone=testone"
        httpRequest.send();//第三步：发送请求  将请求参数写在URL中
        /**
         * 获取数据后的处理程序
         */
        httpRequest.onreadystatechange = function () {
            if (httpRequest.readyState == 4 && httpRequest.status == 200) {
                var json = httpRequest.responseText;//获取到json字符串，还需解析
                console.log(json);
            }
        };

    }